Nielson's survey suggests that paper books are easier to read than iPad books: readers of iPad books read 6.2% slower. However, Kindle readers were 10.2% slower than paper readers. Oddly, both the Kindle and the iPad users rated the experience more enjoyably than paper (the iPad>Kindle>paper scores were 5.8, 5.7, and 5.6; it was a close match, and one wonders about novelty effects – the scores were, after all, in order of device novelty, and relatedly but differently, in order of gizmo sexiness).
iPad also gets top marks for making the computer experience a lot simpler than it used to be. This review pretty much sums up why Apple is able to reach people who never were interested in computers: you don't need to be interested in computers, only in your music or your email or your photos the internet or the like. This is virtually the hallmark of a well-designed tool: you don't notice it really when you use it, just the power it lends you.